The world has become increasingly aware of the scarcity of fuel including, particularly, the fossil fuels, gas and oil. At the same time the world has become increasingly aware of the energy available from the sun, particularly, in those areas where there is a high percentage of days throughout the year when the sun is available for heating purposes and for other energy available in the sun's spectrum. For these reasons, a great deal of attention has been paid to the utilization of solar energy for heating systems and, particularly, for water heating systems.
In those instances wherein it is desired to use the hot water directly, the time interval between the collection of solar energy and its use in the form of hot water is relatively short. In the instances wherein the energy is intended to be used for space heating, as for example, heating of homes, the heating of hot water through the use of solar energy provides a storage means from which the heat can be later extracted for use in space heating.
Solar heating systems can be designed from the ground up so to speak, but frequently the system consists of applying a solar collector, or solar heating unit, to an already existing hot water tank. Typically, this is the case in home systems. Here the federal government regulations require that the solar heating unit be utilized in connection with an existing hot water heater which has its own heating source whether it be electric, gas or oil. Such systems include the solar collecting unit operating in association with a hot water heater or the solar heating unit operates in connection with a heat exchanger that is connected to the hot water heater. The heat exchanger may be a separate unit or it may be part of a larger water tank system. In any event, the liquid flowing through the solar collector which is usually mounted on a roof of a house, has water flowing through it that is heated in the process of being exposed to the sun's radiation. When the ambient temperature drops below freezing, the water circulating through the solar collector unit is apt to freeze and in so doing may burst the pipes in the solar collector. This would incapacitate the system and render substantial damage. Systems for preventing this are known to the art and usually involve the drainage of the solar collector unit, or the circulation therethrough of warm water from the hot water heater itself. Such known systems tend to be large and bulky, complicated and somewhat ineffective in operation. It goes virtually without saying that the possibility of freezing of a solar water heating system is an intolerable situation.
Accordingly, it is an object of the invention to provide an improved solar hot water heating system eliminating the objections of prior art devices.
It is a further object of the invention to provide a solar heating system of the nature indicated including an improved system for drainage of the circulating liquid through the solar collector unit when the ambient temperature drops below a predetermined value.
It is a further object of the invention to provide an improved heat exchanging unit which is small in size and efficient in operation for use in connection with a solar heating system including a solar collector and a water heater.